Jason Derulo knows exactly what he'll do if he comes face-to-face with the Facebook killer.
We got the singer at LAX, and like almost everyone, he's shaken by the horrific story of Steve Stephens posting video of himself murdering a grandfather. Jason says you can't blame social media for this ... Stephens is just sick.
As for the $50k reward to catch the killer -- Jason told us how he thinks America should respond, and says he's ready to back up his words.